The discussion below is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.
In a first aspect the invention relates to a disconnectable mooring system for a vessel, comprising a moonpool in the vessel, a turret structure mounted for a rotation in said moonpool and a buoy member having a plurality of passages each adapted to receive a riser, wherein the turret structure has a lower end comprising a buoy receptacle for detachably receiving the buoy member, and wherein the mooring system further comprises a plurality of mooring lines for transmitting mooring forces and each having a lower end and an upper end connected to the seabed and the buoy member, respectively.
Such a disconnectable mooring system is known from EP-B-1 803 641. Under normal operating conditions the mooring forces in the mooring lines are such that during a disconnect the buoy member may be disconnected from the turret structure and may be lowered in a controlled manner to a position away from the vessel and well below sea level. Under specific circumstances however, for example when the vessel is enclosed by drifting pack ice, a disconnect of the buoy member from the turret structure has to be carried out while extremely high mooring forces are transmitted by the mooring lines to the buoy member. Typically such high mooring forces create an asymmetrical load on the buoy member, such that after a disconnect of the buoy member from the turret structure it would tilt in the buoy receptacle and can cause severe damage to the buoy member, risers, umbilicals and/or surrounding structure of the (turret structure of the) vessel.